The quality of PET images has improved with the use of time-of-flight (TOF) Positron Emission Tomography (PET) technology. However, accurate timing calibration of the detectors is critical for TOF PET systems. An accurate, robust, and not very time-consuming crystal-based timing calibration method is needed to achieve the best timing information for TOF PET.
Existing timing calibration methods include (1) introducing light pulses into the photomultiplier tubes (PMTs) or introducing electrical pulses into the preamplifiers, (2) using a radioactive source embedded in a plastic scintillator coupled to a PMT, (3) using a rotating radioactive line source, and (4) using a radioactive point source in a scattering phantom.
As shown in FIG. 1, conventional timing calibration is performed using coincident 511 keV gamma rays 5 emitted following annihilation of positrons 3 and electrons 4. As shown in FIG. 1, the positron 3 is ejected from the radioisotope 2 with a significant kinetic energy (typically ˜MeV), and travels some distance before annihilation. In the conventional art, generally, the source 1 and material around the source are arranged so that the annihilation occurs in the radioisotope or in the surrounding material, which is typically within a few mm of the positron-emitting isotope 2.